Abstract
SUMMARY Mt Etna lies on the footwall of a large normal fault system, which cuts the eastern coast of Sicily and crosses the volcano eastern flank. These faults are responsible for both large magnitude historical earthquakes and smaller damaging seismic events, closer to the volcano. We investigate here the two-way mechanical coupling between such normal faults and Mt Etna through elastic stress transfer. The comparison between eruptive sequences and historical seismicity reveals that the large earthquakes which struck the eastern Sicily occurred after long periods of activity along the Mt Etna rift zone. The larger the erupted lava volumes, the stronger the earthquake. The smaller earthquakes located on the eastern flank of the volcano occur during periods of rift zone eruptions. We point out that the seismicity rates are well correlated with the rate of erupted lava. By modelling elastic stress changes caused by earthquakes and eruptions in a 3-D elastic half-space, we investigate their interaction. Earthquake dislocations create a vertical stress gradient along fissures oriented perpendicular to the minimum compressive stress and compress shallow reservoirs beneath the volcano. This may perturb the magmatic overpressures in the Etna plumbing system and influence the transport and storage of the magma as well as the style of the eruptions. Conversely, the large rift zone eruptions increase up to several tenths MPa the Coulomb stress along the eastern Sicily normal fault system and may promote earthquakes. We show that the seismic activity of the normal faults that cut the eastern flank of the volcano is likely to be controlled by Coulomb stress perturbations caused by the voiding of shallow reservoirs during flank eruptions.
Highlights
Investigating the mechanical coupling between earthquakes and eruptions is very important to better assess the seismic and volcanic hazard in highly exposed and populated regions
We model the Coulomb stress changes caused by Etna eruptions on the Sicilian normal faults as well as the normal and volumetric stress changes generated by large earthquakes on the Etna plumbing system
We first show and discuss the Coulomb stress changes caused by either rift zone eruptions or magmatic inflation of the storage zones on the faults that ruptured during large historical earthquakes (Table 4, Figs 8 and 9)
Summary
Investigating the mechanical coupling between earthquakes and eruptions is very important to better assess the seismic and volcanic hazard in highly exposed and populated regions. Time correlations between these two phenomena have been observed in numerous regions of the world Several studies have shown that static stress changes imparted by the volcano to faults and by the earthquakes to the volcanoes may have promoted seismic events and volcanic eruptions. A volcanic system, which has reached a critical state, can be perturbed by small stress changes caused by a large earthquake occurred nearby (see Hill et al 2002, and references therein). In Italy, Nostro et al (1998) have shown that large normal faulting earthquakes along the
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